Ketimide complexes of group 4 metals have been reported in the literature--see, for example, the review of titanium chemistry which as prepared in part by one of us in 1982 (Ref: M. Bottrill, P. D. Gavens, J. W. Kelland and J. McMeeking in "Comprehensive Organometallic Chemistry", Ed. G. Wilkinson, F. G. A. Stone, & E. W. Abel, Pergamon Press, 1982, Section 22.3, page 392). However, the use of ketimide ligand/group 4 metal complex as an ethylene polymerization catalyst was heretofore unknown.
Preferred ketimide catalysts of this invention also contain one and only one cyclopentadienyl-type ligand.
The prior art includes many examples of olefin polymerization catalysts having a single cyclopentadienyl ligand most notably the so called Bercaw ligand (*Cp--Me.sub.2 Si--N.sup.t Bu) which was disclosed as a Scandium complex by Bercaw et al in the fall of 1988 and subsequently claimed as a titanium complex in U.S. Pat. No. 5,064,802 (Stevens and Neithamer, to Dow Chemical) and U.S. Pat. No. 5,055,438 (Canich, to Exxon). The use of a titanium complex of the Bercaw ligand provides an olefin polymerization catalyst which has excellent comonomer response--i.e. the catalyst is excellent for the preparation of ethylene/.alpha.-olefin copolymers. However, the bridged structure of the Bercaw ligand is expensive to synthesize. Accordingly, an olefin polymerization catalyst which doesn't require a "bridge" to provide comonomer response would represent a useful addition to the art.